Gift cards don't work?

My kids got Google play gift cards for Christmas this year. I tried uploading and not a single one of them worked, all require additional information, which is irritating. Additional information is pics of the gift card, front and back, and a scanned copy of the receipt! These are GIFTS. I don't have the receipts. Last year all Roblox gift cards didn't work, so I told family to get them Google play this year. Now Google play doesn't work... Anyone else having this issue? My mom found the receipt for one of the gift cards, so we'll try jumping through the hops on that one when I get it.

I'm in Canada, if that matters.